Neuroblastoma (NB) is the most common extracranial malignant solid tumor in children and contributes to more than 15% of all pediatric cancer-related deaths. Despite the overall improvement in the disease outcome, MYCN-amplified (MYCNA) NB largely remains an incurable disease. Unlike in adult tumors, recurrent somatic mutations in NB occur with relative paucity. Therefore, de-regulation of oncogenic signal transduction may contribute to NB tumorigenesis. This proposal will pursue that goal by defining the role and regulation of transmembrane protein 108 (TMEM108) in NB malignancy and examining the effect of TMEM108 inhibition on NB cell proliferation and tumor growth in an orthotopic mouse model. TMEM108 is a potential cell surface receptor-like protein with a signal peptide sequence at the N-terminal for protein secretion and an extracellular domain and intracellular domain separated by a transmembrane sequence. TMEM108 is highly overexpressed in NB tumor samples and its overexpression significantly predicts poor patient outcome in the Versteeg-88 data set (R2: http://r2.amc.nl). TMEM108 is a completely uncharacterized gene that is enriched in NB tumors and cell lines. In our preliminary studies, we have found that knockdown or knockout of TMEM108 expression caused a cell proliferation defect in one MYCN-amplified and one MYCN-non-amplified NB cell lines. In addition, we also found that overexpression of TMEM108 mutant (mt) with the deletion of its intracellular domain inhibited NB cell proliferation compared to vector control and TMEM108 full-length wild-type (wt). Rabbit polyclonal antibodies targeting its extracellular domain inhibited NB cell proliferation in culture and tumor growth in an orthotopic xenograft mouse model. These findings strongly suggest that TMEM108 mediates an oncogenic signaling pathway in NB cells. Therefore, targeting TMEM108 extracellular domain by an inhibitory antibody or its downstream signaling pathway has a great potential to be eastablished as novel treatment options for NB patients. The central hypothesis of this work is that TMEM108 is an ideal molecular target in NB for an antibody- based therapy. The proposed experiments will test this hypothesis by determining the effect of TMEM108 inhibition on NB tumor growth in cell culture and in an orthotopic mouse model. The specific aims for this project are: 1) to determine the function of TMEM108 in the regulation of NB malignancy; and 2) to determine the therapeutic potential of TMEM108 inhibition in vivo. Targeting TMEM108 is a novel concept in the future treatment of NB. The proposed project, if successful, will establish TMEM108 as a therapeutic target in NB. TMEM108 inhibition may serve not only as a stand-alone therapy but also as an effective adjunct to current chemotherapeutic regimens for treating this aggressive pediatric malignancy.